Performance to expect from an iMac G5 1.8 20" ALS

Discussion in 'PowerPC Macs' started by monkeybagel, Sep 25, 2011.

  1. monkeybagel macrumors 65816

    Jul 24, 2011
    United States
    I received an iMac for some work I did for someone and was told it was in good working order. This is my newest PowerPC-based product and started off the Macintosh hobby working backward (interest in their current products caused me to research their older products).

    Anyway - the machine seems slower than it should and does not seem to be running correctly. From the reading I have done, it seems this model has some cooling problems on occasion and capacitor issues as well. I think the caps are okay as I have not seen any leaking ones.

    My observations thus far are-

    - Very noisy fan. Starts off slow during boot process and by the time the machine boots and I launch an application or two, it is very audible. A whirring sound. Especially does this when doing really anything in Safari or Entourage. CPU temp approaches 60-62 degrees C and fan picks up to about 3k just writing this post. CPU Performance is currently set to Highest as the machine was running so slow IMO. Automatic and Reduced, of course do lower the temps and slow down the fans, at a great cost in performance. I am trying to get a feel for if this is expected behavior.

    - Very picky on RAM chips, or a bad RAM socket. When I received the computer it had I believe 1GB of RAM in it. At first, it would allow me to install Tiger without issue. However the Leopard installation would not even finish with a panic. I tried several times, and could not get it to work. It was actually usable in Tiger however Leopard would crash almost always during the install process. I suspected a hardware issue so I ran AHT and it informed me that a module was bad. I replaced the module with a spare I had, and got the same results (leading me to believe it is a bad slot). Also, a few bad sectors were located on the hard disk, so I replaced the hard disk as well. Not wanting to put too much money in it, I am reluctant to order two 1Gb modules since I am unsure how it is going to turn out. It is currently running with 512MB or RAM in one slot and is very stable - just noisy and warm.

    I blew out any vents inside and the CPU channel/heatsink as well as remove excess dust. The computer is very clean inside.

    I reset the PRAM and SMC and could tell no difference.

    Currently, I only have open Safari as the only application. If I drop down to the Dock and click System Preferences, the fans speed up a great deal while the window is drawing and the machine gets much louder.

    For comparison, I have a very old (for parts and tinkering mainly) Power Macintosh G4 dual 450 with 1GbE and it seems as fast (or faster) as the G5 (which doesn't sound right to me). Another Power Macintosh (AGP Graphics) single processor seems faster too. These both have 1GB of RAM in them.

    The only things that come to mind is perhaps 1) I am expecting too much from this machine and it is normal for the fan to speed up when launching any app such as System Preferences, 2) There is a heatsink issue that needs to be addressed and additional thermal paste needs to be applied or cleaned, or 3) There is a logic board issue.

    Would love to hear some input from some folks with more PPC experience than me. I am running Leopard .8 right now, but also get similar results with Tiger .11. With Tiger, the system doesn't seem to be under the same load so the fan is not quite as loud and it is slightly more responsive, which I think is to be expected since it is a "lighter" OS, especially in terms of the GUI.

  2. Jethryn Freyman macrumors 68020

    Jethryn Freyman

    Aug 9, 2007
    It should most certainly be faster than the dual 450 Power Mac you have... but those G5 iMacs had totally appalling reliablity (capacitor problems.)
  3. mabaker macrumors 65816


    Jan 19, 2008
    I got a second generation iMac G5 ALS with 2.0 GHz and it is a overheating magnet, as well. But the three fans inside do manage to cool it pretty well.

    I do suspect it's a heat issue in your case where the system throttles down the CPU heavily thus causing the slow overall performance. The only thing I would recommend is to apply these extreme measures:

    Is it's not your main working machine then I am not sure if it's worth the effort. 20"s are very sweet machines with huge real screen estate and a G5 to handle even the most demanding websites but it's up to you if you're willing to put much into it.
  4. monkeybagel thread starter macrumors 65816

    Jul 24, 2011
    United States
    Thanks for the replies.

    It looks like removing that heat sink can be fairly in-depth, but it does seem like the CPU may be throttling back to prevent overheating. I do wonder if the thermal paste is dried or is over/under applied.

    Is there a possible utility to monitor the clock speed of the processor in real time?

    It is not my main machine - mainly just something to tinker on. I may try to remove the heatsink when I have some spare time and see what I find because it is not a very usable machine the way it is right now.

    Luckily I really haven't invested any money in it since I had the spare hard disk and RAM.

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